Method and device for automatic testing of an X-ray system

ABSTRACT

The invention relates to a method and a device for automatic testing of an X-ray system ( 2 ). The doors ( 5   a,    5   b ) leading to the room ( 1 ) in which the X-ray system ( 2 ) is installed are monitored by way of sensors ( 4   a,    4   b ). Furthermore, the state of the room ( 1 ) can be monitored by means of further sensors such as video cameras ( 3 ). Automatic testing of the X-ray system ( 2 ) while utilizing X-rays is started only if and for as long as all doors are closed and the other sensors do not indicate that a safe state is abandoned. The device may also include facilities for automatically positioning a phantom in the beam path. Such facilities may in that case include a phantom which is provided on a flexible foil.

The invention realtes to a method as well as to a device for automatictesting of an imaging X-ray system while generating X-rays.

Imaging X-ray systems are widely used in the medical field as well as inother applications such as the testing of materials. They include anX-ray source for generating X-rays which irradiate an object to beexamined and are subsequently detected by an X-ray detector.

The parameters of such X-ray systems which are of decisive importance inrespect of the actual imaging tend to drift in the course of time.Generally speaking, such drift leads to a deteriorated performance ofthe imaging system. For example, when the image quality of a medicalX-ray system has deteriorated beyond a given limit, the X-ray systemwill be tested by technicians upon request by the hospital staff. Suchtesting includes the acquisition of gain images and other calibrationimages. Because X-rays must be generated so as to acquire the images,for reasons of safety the test procedure must be monitored continuouslyby qualified personnel. It is to be noted in this respect that, forexample, in the case of a flat dynamic X-ray detector (FDXD), a gaincalibration requires approximately twenty minutes for a combination ofgain and mode; during this entire period an operator must be present soas to prevent radiation accidents and to exchange test phantoms. Infuture generations of detectors, typically involving seven modes andfour sets of gains, the calibration duration overall will even amount toseveral hours. During a test, however, not only time and work have to bespent by the staff directly involved, but costs are also incurred andproblems arise because of the fact that the X-ray system cannot be usedfor its normal duties. Because of these problems, recalibration of thesystem is carried out only comparatively rarely nowadays, meaning that agiven deterioration of the image quality has to be tolerated.

In order to accelerate and simplify the testing of the image quality ofan X-ray system, EP 0 874 536 A1 proposes a specially configuredphantom. A phantom is to be understood to mean an object of known shapeand structure which for test purposes can be introduced into the beampath between the X-ray source and the X-ray detector in order todetermine how it is imaged by the X-ray system. The phantom proposed inEP 0 874 536 A1 is arranged especially to enable measurement of givenaspects of the image quality, such as the resolution and contrast, in asingle X-ray image. However, it does not enable more comprehensivetesting of the X-ray system.

Considering the foregoing it is an object of the present invention toprovide a method, a system and a device for testing an imaging X-raysystem which enable significantly simpler and more economical testing.

These objects are achieved by means of a method as disclosed in thecharacterizing part of claim 1, by a method as disclosed in thecharacterizing part of claim 5, by a device as disclosed in thecharacterizing part of claim 6, by a device as disclosed in thecharacterizing part of claim 8, by an apparatus as disclosed in claim 11and by a system as disclosed in claim 14. Advantageous furtherembodiments are disclosed in the dependent claims.

In conformity with a first aspect, the invention relates to a method forthe automatic testing of an imaging X-ray system while generatingX-rays, the testing being understood to mean here and hereinafter aself-test, a recalibration for the compensation of parameter drifts, thestart of an algorithm or a search tree for fault finding or the like.While the method is being carried out, the preservation of a definedsafe state in a safety zone around the X-ray system is monitored bymeans of at least one sensor, and the generating of X-rays isinterrupted if said safe state is abandoned.

Because of the automatic monitoring by means of the at least one sensor,the proposed method ensures that a safe state is maintained around theX-ray system while the test is being carried out, so that humans cannotbe endangered by the X-rays generated. Such automatic monitoring of thesafety is a prerequisite for automation of the testing of the overallX-ray system such that the continuous presence of a technician can bedispensed with.

In conformity with a preferred version, the closed state of at least oneaccess which leads directly or indirectly to the safety zone around theX-ray system and can be opened and closed per definition forms part ofthe safe state. The safety zone can then be defined notably as the roomin which the X-ray system is installed and the access may be formed by adoor, a window or the like. Preferably, the safe state involves theclosed state of all accesses leading directly or indirectly to thesafety zone, for example, the closed state of all doors of the room inwhich the X-ray system is installed. The monitoring of the doors leadingto the X-ray system ensures that no person can accidentally enter thezone around the X-ray system while the method is being carried out;otherwise such a person would be exposed to hazardous X-rays. Thepresence of a technician can in that case be limited to a starting phaseof limited duration in which it is ensured that no person is present inthe room in which the X-ray system is installed.

In conformity with a further version of the method the pattern of sensorsignals determined or observed during a definition phase is used todefine the safe state of the environment of the X-ray system. The methodcan thus be flexibly adapted to different locations of use (for example,different hospitals) in that each time different patterns of sensorsignals are observed. Under the supervision by a technician, a givenpattern of sensor signals can then be defined as that of the safe state,after which the subsequent monitoring of the preservation of the safestate can take place automatically.

In a further preferred version of the method the monitoring of the safestate commences when firstly all doors leading directly or indirectly tothe room in which the X-ray system is installed (including otheraccesses for persons) have been closed (and remain closed) except forone door, and when secondly an activation signal associated with thelast door commences while the last door is still open and ends when thelast door is closed. For example, such a procedure allows a technicianwishing to start the automatic test method to close all access doors tothe room in which the X-ray system is installed, except for a last door,while making sure that there is not other person present in this room.After this condition has been satisfied, the technician can initiate,for example, by way of an actuation button provided on the outside ofthe last door, a signal while the last door is still open and sustainthis signal until the last door has been closed. The provision of theactuation button outside the room in which the X-ray system is installedensures that the technician has then also left the room.

In conformity with a second aspect the invention relates to a method forthe automatic testing of an imaging X-ray system while generatingX-rays, in which a phantom is automatically introduced into the spacebetween the X-ray source and the X-ray detector during the test and atleast one image is acquired while the phantom is present in the beampath. Preferably, in addition at least one image is acquired while thephantom is not present in the beam path. Furthermore, during an exposurethe phantom can also be automatically moved in the beam path between theX-ray source and the X-ray detector, so that time effects can beinvestigated.

A method of this kind is carried out preferably in combination with amethod of the kind described above, that is, with sensor-basedmonitoring of a defined safe state of the environment of the X-raysystem and with automatic interruption of the X-rays when the safe stateis abandoned.

The automatic introduction of the phantom in the beam path enablesvarious calibration images to be formed without it being necessary foran operator to exchange or remove the phantom by hand. The entiretesting process can thus be performed automatically, for example, duringthe night. Furthermore, the different positioning or the movement of thephantom in the zone between the X-ray source and the detector enables aspatially resolved examination of the image quality, because the phantomcan be arranged in different positions within the imaging zone. This inturn enables a diagnosis and localization of defective components in thedetector, so that fault finding can be performed prior to the dedicateddeployment of service personnel. Furthermore, it is feasible that afterthe execution of the test method, maintenance is requested actively orautomatically if such maintenance appears to be necessary on the basisof the test results.

The invention also relates to a device for automatic testing of animaging X-ray system while generating X-rays, which device includes thefollowing elements:

-   a) at least one sensor for monitoring a safety zone around the X-ray    system, and-   b) a control unit which is coupled to the sensor and to the X-ray    system and is arranged to interrupt the generating of X-rays when    the sensor signals indicate that a defined safe state is abandoned.

The invention preferably includes actuation elements whereby the testingof the X-ray system can be started and/or interrupted. The device issuitable for carrying out a method in conformity with the first aspectof the invention, so that automatic testing of the system can beachieved while safety is ensured at the same time.

The sensors for monitoring the environment of the X-ray system maynotably include one or more of the following sensors:

-   Door contacts for detecting the closed state of accesses such as    notably doors.-   Motion detectors for detecting a motion taking place in the vicinity    of the X-ray system, so that notably the undue presence of a person    in the vicinity of the X-ray system can be detected. Such motion    detectors may operate on the basis of infrared signals, ultrasound    signals (for example, while utilizing the ultrasound Doppler effect)    and/or video signals which can be analyzed by means of image    processing software for the detection of changes in the image.-   Gas detectors whereby a change of the atmosphere in the safety zone    can be recognized. Such detectors may notably be carbon dioxide    sensors which detect an increase of CO₂ due to the respiration of a    person present.-   Pressure sensors which are capable of detecting contact by a person    present in the safety zone. Notably mats on the floor may be    provided with load detectors which initiate a signal when stepped    upon.-   Light barriers which are capable of detecting an interruption due to    a person present in the beam path. The light barriers can extend,    for example, through the room in the vicinity of the X-ray system    and be deflected a number of times by reflective surfaces on their    way from the source to the detector. Furthermore, the safety zone    can be very narrowly limited to the radiation zone (radiation cone)    of the (primary) X-rays while the borders of this safety zone are    monitored by a dense network of light barriers or by a light barrier    surface. Transgression of these borders would then lead immediate    switching off of the X-rays, so that the object invading the safety    zone would no longer be exposed to danger. Preferably, the light    barriers operate in a pulsed mode, for example, at a frequency of    300 Hz, in order to enable reliable discrimination between their    signal and background light.-   An acoustic sensor, for example, in the form of a microphone with a    monitoring system connected thereto.-   The X-ray detector of the X-ray system, in which case an object    invading the beam path would be recognized on the basis of the    resultant change of the X-ray image. To this end, for example, an    image analysis system could detect any deviation from the expected    image and initiate the switching-off of the X-rays in response    thereto.

Finally, the invention also relates to a device for the automatictesting of an imaging X-ray system while generating X-rays, Whichtesting device includes a device for the automatic positioning of atleast one phantom in the zone between the X-ray source and the detector.A device of this kind is suitable for carrying out the described methodin conformity with the second aspect of the invention in which at leastone image is acquired by means of the phantom.

In conformity with a first embodiment, the phantom may be provided on aflexible carrier, for example a foil or a wire, the carrier beingtransported, via guide rollers, in the zone between the X-ray source andthe X-ray detector. Activation of drive rollers enables concertedmovement of such a flexible carrier in a simple manner, so that thephantom can be positioned in front of the detector as desired. Theflexible carrier can be transported in the form of an endless loop via aplurality of guide rollers, or be wound onto and from a roller at bothits ends.

In conformity with a further embodiment, the phantom is journaled so asto be pivotable about a pivot axis, so that it can be moved to, or bepositioned differently in, the beam path between the X-ray source andthe X-ray detector by way of a simple pivoting motion.

The invention will be described in detail hereinafter, by way ofexample, with reference to the Figures. Therein:

FIG. 1 is a diagrammatic representation of the vicinity of an X-raysystem which is monitored by means of the method in accordance with theinvention;

FIG. 2 shows a first embodiment of a phantom which is provided on aflexible foil, the foil being transported in the form of an endlessloop;

FIG. 3 shows a second embodiment of a phantom provided on a flexiblefoil, the foil being wound onto rollers at its ends and it beingpossible to move the phantom to a lateral position,

FIG. 4 shows a third embodiment of a phantom provided on a flexiblefoil, the foil with the phantom being wound onto rollers at its ends;

FIG. 5 shows a fourth embodiment of a phantom provided on a flexiblefoil, the foil being wound onto rollers at its ends and it beingpossible to position the phantom in a non-sensitive zone adjacent to thedetector;

FIG. 6 shows various feasible arrangements of the phantoms of the FIGS.2 to 5 in a plan view;

FIG. 7 shows a side elevation and a plan view of a fifth embodiment witha phantom formed by a wire, and

FIG. 8 shows a phantom which is arranged so as to be pivotable at theedge of an X-ray detector.

FIG. 1 is a diagrammatic representation of the environment of a medicalimaging X-ray system 2 which may be, for example, an X-ray catheterlaboratory or also a computed tomography apparatus. It is necessary totest an X-ray system of this kind from time to time; such a test mayinclude notably a recalibration for the compensation of parameterdrifts, but also a self-test or an automatic fault diagnosis. A test ofthis kind should be carried out without risks to the hospital staff,patients or other persons and, because the duration of the testtypically amounts to several hours, it should be carried out withoutconstant monitoring by an operator.

In order to automate a test method and to ensure the safety, theinvention proposes a device which is capable of interrupting, ifnecessary, the test at any instant so as to change over to normaloperation and which, moreover, is capable of carrying out all operationsnecessary for the test, notably the positioning of a phantom in the beampath. An automatic method for the testing of system components whichrequire X-rays for calibration (for example, gain calibration) can makea substantial contribution to the reduction of the operating costs andthe need for staff and at the same time ensure an imaging performancewhich is stable in time.

Probably the most important problem encountered in the automation oftest tasks of an X-ray system while generating ionizing radiationconsists in ensuring that persons cannot be unintentionally andaccidentally exposed to the X-rays. Persons that could be endangeredare, for example, cleaning staff, physicians preparing the examinations,technicians and/or patients on their way through the hospital or to anexamination.

In this respect FIG. 1 shows, by way of example, a device in accordancewith the invention for the prevention of radiation accidents. The X-raysystem 2 to be tested is installed in a room 1 which can be accessed viatwo doors 5 a and 5 b. The room 1 is adjoined by a control room 6wherefrom the X-ray system 2 can be controlled. In accordance with theinvention, prior to the automatic testing of the X-ray system 2 aqualified human operator verifies that a safe state exists in a safetyzone around the X-ray system 2 (that is, in the room 1). Subsequently,this safety state is “preserved” in a sense that all relevant changes ofthe safe state are automatically detected and automatically give rise toan immediate stop of the generating of X-rays as well as to a reset ofthe system to the standby state. This behavior is achieved essentiallyby means of three system components:

-   Monitoring sensors at all entrances to the room 1 in which the X-ray    system 2 is installed. In the device shown in FIG. 1 these    monitoring sensors are realized in the form of door contacts 4 a and    4 b which can detect and inform the control room 6 as to whether the    doors 5 a and 5 b are closed or not.-   A control element for starting the automatic test procedure, which    element may be realized, for example, in the form of a “CALIBRATION    ENABLE” button 7 in the control room 6.-   A control unit 9 which is connected to suitable sensors such as the    door contacts 4 a, 4 b and is arranged to detect a breach of the    isolation of the room 1 as well as to deactivate the X-ray system 2    in response thereto. The sensors may also include, for example, one    or more video cameras 3 with appropriate image analysis software    enabling the detection of changes in the images of the room 1.    Furthermore, infrared or Doppler ultrasound motion detectors, gas    detectors, a microphone, light barriers or the like may also be    connected to the control unit 9 (not shown). Moreover, the detector    of the X-ray system 2 may be coupled to a (comparatively simple)    image analysis device which detects the presence of unexpected    structures in the X-ray image. For example, it could be detected if    a hand of a person present in the room were to invade the beam path    of the active X-ray system 2.

The device shown in FIG. 1 can be set to a self-test/calibration modewhen all doors 5 a, 5 b to the room 1 are closed and the “CALIBRATIONENABLE” button 7 in the control room 6 is pressed. The test radiation isthen released after visual inspection of the room 1 by an authorizedphysician, a technician or other person authorized to carry out X-rayexaminations or calibrations.

If, as opposed to the situation shown in FIG. 1, there is no controlroom 6 enabling complete visual inspection of the X-ray system 2,preferably, the “CALIBRATION ENABLE” buttons 7 are provided at eachentrance. In this arrangement the physician or technician must keep thebutton 7 depressed during the closing of the door so as to generate anactivation signal. This activation signal is considered to be valid bythe control unit of the system when firstly all entrances but one areclosed when the button is depressed and remains closed during the entirepreservation procedure, and when secondly the door neighboring thebutton is open when the button is depressed and closed when the buttonis released.

In response to said activation signal, the control unit starts to checkthe state of all safety points at the entrances to the room 1 in whichthe X-ray system 2 is installed. If the “sealing” of the room 1 is inorder, the sensors present monitor the state of the room for a givenperiod of time so as to acquire a pattern of sensor signals associatedwith a normal, undisturbed safe state of the X-ray room. The pattern mayinclude measurements of a series of sensors, use preferably being madeof an inexpensive video camera 3 in conjunction with standard softwarefor image processing. After the sensor pattern of the safe state hasthus been acquired and tested for consistency as well as slow changes intime, the calibration procedure is started.

The calibration procedure is terminated again when one of the followingconditions is satisfied:

-   1. A “CALIBRATION DISABLE” button 8 arranged in the vicinity of the    “CALIBRATION ENABLE” button is depressed.-   2. One of the doors 5 a, 5 b of the sealed room 1 is opened.-   3. The control unit detects, by way of the connected sensors 3, a    suspicious activity in the sealed room 1, for example, on the basis    of deviations from the acquired sensor pattern which are caused by a    motion.

In the case of such an interruption, the device returns to a standbystate in which it is ready again for image acquisition.

Preferably, at all entrances 5 a, 5 b there are provided alarm signalswhich indicate the X-ray activity so that unintentional interruption ofthe calibration or the self-test by a person entering the room isextremely unlikely.

In order to minimize the necessity of control interventions, the deviceshould be capable of automatically executing as many activities aspossible for a self-test. Whereas an automated gain calibration requiresonly an initialization of the SID (Source Image Distance) and thecollimator position (if it is not yet automated), the testing of theoperational behavior of the system and the entry into a search tree forfault finding require one or more phantoms in the vicinity of thedetector. Hereinafter, various arrangements for automaticallypositioning test phantoms for testing the modulation transfer function(MTF) and the DQE (Detective Quantum Efficiency) into the beam path willbe described in detail hereinafter with reference to the FIGS., 2 to 8.

FIG. 2 is a cross-sectional view of an X-ray detector with anX-ray-sensitive layer 10, the phantom 23 being provided on a foil 11 ofa synthetic material. The synthetic foil 11 is guided in an endless looparound the sensitive layer 10 by way of four guide raflers 22; in thesituation shown, the phantom 23, being made of flexible lead, issituated in the standard position underneath the detector, that is, notin the beam path. When a test is carried out, the foil 11 with thephantom 23 on the upper side can be moved in front of the sensitivelayer 10 by driving at least one of the rollers 22, so that the phantomis situated in the beam path from the X-ray source to the detector. TheX-ray source is an X-ray beam 130 represented by a line of dots anddashes being propagated on an axis 140. The beam emanates from a focus150 situated in an X-ray tube not represented.

FIG. 3 is a cross-sectional view of an alternative embodiment of thedescribed device; as opposed to FIG. 2, the carrier foil 11 is notguided in an endless loop but is wound around a respective roller 32 atboth its ends. In the standard state the phantom 33 is situated to theside of the sensitive surface 10. The phantom 33 can be positioned infront of the surface of the detector by unwinding the carrier foil 11from one roller and onto the other roller 32. The arrangement shownoffers easy access to the detector from the rear thereof.

FIG. 4 shows a further embodiment of the described device in which thephantom 43 and the carrier 11 are wound together onto a roller at theside of an end when it is not to be positioned in front of the sensitivesurface 10.

FIG. 5 shows a further embodiment of the device of FIG. 3 in which thephantom 53 is arranged in a zone adjacent to the sensitive surface 10 inthe front plane of the detector when it is not in use. This arrangementoffers the advantage that the phantom 53 need not run over a kink of thecarrier foil 11 so as to be removed from the position in front of thesensor surface 10.

The foils 11 shown in the FIGS. 2 to 5 may also cover less than theentire width of the detector so as to enable easy access to the wiringand the cooling system. FIG. 6 shows, in a plan view, three examples offeasible arrangements of carrier foils 11. In the version a)approximately half the detector surface 10 is covered by a foil 11; inthe version b) parts of the detector surface are covered by two foils,and in the version c) the entire detector surface is covered; the latterversion necessitates lateral access to the wiring of the detector.

FIG. 7 shows an alternative embodiment of a phantom which is formed by awire 73. The ends of the wire 73 are attached to a carrier wire 71, thecarrier wire being guided, like the foil 11 in FIG. 2, around thesensitive surface 10 in an endless loop. The wire 73 can thus bepositioned at option in front of the surface 10 or be removed from thebeam path by rotating at least one of the rollers 72 about itslongitudinal axis.

FIG. 8 shows a further embodiment of an automatically movable phantom.This figure is a plan view of the sensitive surface 10 of an X-raydetector. The strip-like phantom in the standard position (reference 83)is arranged so as to be pivotable about a point 81 in the vicinity ofthe sensitive surface 10. If required, it can be automatically rotatedabout the pivot axis extending perpendicularly to the plane of drawingand hence be introduced into the beam path between the radiation source(not shown) and the sensitive surface 10 (position 83′).

The device described with reference to the Figures enables automaticadaptation of parameters such as, for example, gain settings, withoutendangering the hospital staff, patients or other persons and whilerequiring at the same time only a minimum amount of human supervision.The automatic X-ray calibration can even be performed during the nightin the absence of all personnel, thus reducing the costs of maintenanceand ensuring an imaging performance which is stable in the course oftime.

The invention also enables a purely image-based detection of variousfaults of components of the X-ray system such as faulty pixels, rows orcolumns which occur, for example, due to faulty wiring, transistors orline drivers, faulty AD converter chips, corrosion of the scintillatorlayer, a defective X-ray tube, etc.

1. A method for automatically testing an X-ray imaging system whilegenerating X-rays, comprising the steps of: introducing automatically aphantom into a space between an X-ray source and an X-ray detectorduring a test; acquiring at least one image while the phantom is presentin the beam path; monitoring a defined safe state in a safety zonearound the X-ray system by means of sensors; and interrupting thegeneration of X-rays upon detection that the safe state is abandoned. 2.A method as claimed in claim 1, wherein the safe state involves theclosed state of at least one entrance to the safety zone.
 3. A method asclaimed in claim 1, wherein the safe state is defined by a pattern ofsensor signals observed during a definition phase.
 4. A method asclaimed in claim 1, wherein the monitoring of the safe state commenceswhen all doors leading to the room in which the X-ray system isinstalled are closed except for a last door, and an activation signalassociated with the last door commences while the last door is stillopen and ends when the last door is closed.
 5. A device for theautomatic testing of an imaging X-ray system while generating X-rays,which device comprises: a device for automatically positioning at leastone phantom in a beam path between an X-ray source and an X-ray detectorwhile the test is being carried out; at least one sensor for monitoringa safety zone around the X-ray system; and a control unit which iscoupled to the sensor and to the X-ray system and is arranged tointerrupt the generating of X-rays when the sensor signals indicate thata defined safe state is abandoned.
 6. A device as claimed in claim 5,wherein the sensors include: door contacts for detecting the closedstate of entrances; motion detectors which operate on the basis ofinfrared signals, ultrasound signals and/or video monitoring; gasdetectors, notably carbon dioxide sensors; pressure sensors which may bearranged notably on the floor; light barriers; acoustic sensors and/orthe X-ray detector of the X-ray system.
 7. A device as claimed in claim5, wherein the phantom is arranged on a flexible carrier which istransported, via guide rollers, in the zone between the X-ray source andthe X-ray detector.
 8. A device as claimed in claim 5, wherein thephantom is journaled so as to be pivotable about a pivot axis.
 9. Anapparatus for automatically testing an X-my imaging system whilegenerating X-rays comprising: means for automatically introducing, whilea test is being carried out, a phantom into an area of the X-ray imagingsystem between a source of X-rays and a detector of X-rays; means formonitoring a defined safe state in a safety zone around the X-rayimaging system by means of sensors; and means for interrupting thegeneration of X-rays upon detection that the safe state is abandoned.10. The apparatus of claim 9, wherein the means for automaticallyintroducing a phantom comprises guide rollers.
 11. A system forcalibrating a radiation detecting apparatus, comprising: an activationsystem for enabling an operation of a calibration procedure; a phantomthat is configured to be automatically positioned in an area between aradiation source and a radiation detector during the calibrationprocedure; at least one sensor for monitoring integrity of a predefinedsafety area around the radiation detection apparatus to be calibrated;and a control system operatively coupled to the at least one sensor andconfigured to interrupt the calibration procedure based upon a breach ofthe integrity of the predefined safety area.
 12. The system of claim 11,further comprising a plurality of sensors for monitoring the integrityof the predefined safety area around the radiation detection apparatusto be calibrated.
 13. The system of claim 12, wherein at least one ofthe plurality of sensors is selected from the group consisting of anultrasound motion detector, an infrared motion detector, a video camera,a gas detector, a pressure sensor, a light barrier, an acoustic sensorand a radiation detector.